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| Book/Report | FZJ-2018-02566 |
1985
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18251
Report No.: Juel-2028
Abstract: This overview is nöt intended as yet another contribution to existing reviews on the physics of sputtering and its history. In this respect, the interested reader is referred to the excellent recent monographs and conference proceedings given in Ref. 1 to 5. The intention of this article is to give an introduction to physical sputtering, guided by the interplay between collisional and "thermal" sputtering which has obscured the understanding of the phenomenon since its discovery. It will become apparent that angular distributions of sputtered particles have always played a decisive role in identifying the relevant mechanisms, energy distributions have allowed quantifying them, and mass distributions now urge further efforts towards understanding collective processes. Sputtering of solids is the emission of surface atoms upon impact of energetic radiation. If we restrict ourselves to metals and semiconductors, "radiation" means particle radiation, first and foremost ion radiation. The phenomenon was discovered in studies of electrical gas discharges about 130 years ago. It took half a century before the nature of the particles involved - ions and electrons in the plasma, to name the modern terms - became clear /6,7/, but from this time on the understanding of sputtering (of cathodes) developed much faster. During the first decade of this century STARK suggested two seemingly opposing mechanisms of surface-atom ejection; it has required intensive research up until recently before a clear answer in favour of one or the other could be given. STARK perceived cathodic erosion by ion impact as either an evaporation/sublimation process from a hot micro-spot /6/, or as a result of a succession of binary collisions during which part of the initial (inwardly-directed) momentum is directed back towards surface atoms /8/. A thermal mechanism for sputtering was first proposed by HITTORF /9/ who understood cathodic erosion as plain sublimation from cathodes heated in the gas discharge - thus overriding the statement of his former teacher PLOCKER that particle emission from cathodes is not coupled to the discharge power /10/. GRANQUIST /11/ eventually disproved sputtering as a bulk sublimation process by showing that the yield from externally heated cathodes is largely independent of temperature. - KOHLSCHOTTER /12/ reviewed the early development up to 1912 and concluded by renouncing his own model in favour of STARK's. The concept of a hot spot developing around the projectile's point of impact was pursued in various areas of radiation/condensed-matter interaction : by DESSAUER in radiation biology ("Punktwärmetheorie", /13/), by KAPITZA in ion-induced electron emission /14/ and by v. HIPPEL in sputtering /15/.
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